Atrial fibrillation (AF) is a form of heart disease that afflicts millions of people. It is a condition in which the normal contraction of the heart is interrupted, primarily by abnormal and uncontrolled action of the atria of the heart. The heart has four chambers: the right atrium, right ventricle, the left ventricle, and the left atrium. The right atrium pumps de-oxygenated blood from the vena cava to the right ventricle, which pumps the blood to the lungs, necessary for return flow of de-oxygenated blood from the body. The right atrium contracts to squeeze blood into the right ventricle, and expands to suck blood from the vena cava. The left atrium pumps oxygenated blood from the pulmonary veins (returning from the lungs), necessary for flow of oxygenated blood from the lungs. The left atrium contracts to squeeze blood into the left ventricle, which then pumps the blood into the aorta and thence to the entire body, and expands to suck blood from the pulmonary veins. The contractions of the atria normally occur in a controlled sequence with the contractions of the other chambers of the heart. When the left atrium or the right atrium fails to contract, contracts out of sequence, or contracts ineffectively, blood flow within the heart is disrupted. The disruption of the normal rhythm of contraction is referred to as an arrhythmia. The arrhythmia, known as atrial fibrillation, can cause weakness of the heart due to reduced ventricular filling and reduced cardiac output. Stroke due to clot formation in a poorly contracting atria (which may lead to brain damage and death), and even other life threatening ventricular arrhythmias can also occur.
There is a broad spectrum of situations which fall under the broad heading of AF. For example, in older patients where there is substantial heterogeneity in the conduction within the atrial tissue, the patient is said to have the tissue substrate for AF such that any trigger will result in maintaining AF. In younger patients, the tissue may have more homogeneous conduction and be less likely to have sustained AF. In the younger patient it may be the often reoccurrence of a premature depolarizing tissue which acts as a trigger that causes the clinical manifestation of problematic episodes of AF. Clearly, there is a continuous spectrum of degrees of triggered AF and conduction heterogeneity which acts as a substrate for this arrhythmia, and it is appropriate that a number of medical therapies are being developed to treat and diagnose this disease.
Atrial fibrillation can be treated by atrial ablation. There are two general approaches for providing ablative therapy to the heart for the treatment of atrial fibrillation. These shall be called the long linear ablative lesion approach, and the focal ablation approach.
In the long linear lesion approach, the heart tissue is killed along a linear pathway. The cardiac electrophysiologist does this to segment the heart into regions which are too small to sustain atrial fibrillation. Such an approach is very similar to performing the Maze procedure using radiofrequency, microwave, and ultrasound ablative energy sources on the end of catheters. In the Maze procedure, a number of incisions are made with a scalpel in an attempt to terminate inappropriate accessory pathways.
In the focal ablation approach, the heart tissue is killed at a single site. The cardiac electrophysiologist attempts to ablate the region of the heart that prematurely depolarizes, and which has been described as acting as a trigger for the initiation of atrial fibrillation. Recently, ablation of the junction of the pulmonary veins and the left atrium has been performed. Such ablations remove the possibility of triggers for AF initiating within the pulmonary veins, or at the region near the junction of the veins with the left atrial tissue. Such ablations may also remove disturbances introduced into the conduction pathway by the heterogeneity of the junction region anatomy.